This invention relates to improvements in linear motion ball bearing units.
The linear motion ball bearing unit, which has the balls held inbetween R-grooves of a precision-machined track shaft and load carrying ball grooves of a race cylinder of the bearing for circulation in an endless manner to and from load carrying and non-load carrying ball grooves of the race body through ball guide U-grooves of end lids, ensures light and smooth motions even in preloaded state without involving frictional wear of sliding parts, so that it is suitable for applications to those machines which require high positioning accuracy as well as repeating accuracy and rigidity, for example, to machining centers, X-Y-Z guides of various NC machine tools, electric discharge machines, high speed presses, precision press ram guides, press die exchangers and diversified kinds of weight transfer devices.
Generally, with a bearing unit which is provided with a plural number of drilled grooves in its casing for circulation of non-load carrying balls in the axial direction (U.S. Pat. No. 4,127,309), an increase in cost is unavoidable due to the difficulty of speeding up the drilling operation with use of existing drilling tools.
On the other hand, in a case where the non-load carrying ball grooves are formed in a casing itself, it becomes necessary to use a casing of a large wall thickness. (U.S. Pat. No. 4,040,679). This results in a bearing unit construction which is large-sized in height from the lower side of the track shaft to the top of the casing. In this instance the bearing is greatly influenced by lateral and upward loads and its application is limited to some extent.
In an attempt to eliminate these problems, the present inventors disclosed in their prior application (now U.S. Pat. No. 3,897,982) a slide way bearing which incorporates an outer sleeve in a tunnel-like recess of a casing. This bearing construction, however, requires a complicate fabrication process for forming the ball grooves in both the outer sleeve and the retainer for the guidance of the non-load carrying balls.